First-time donors provide 30.9% of all blood donations. Unfortunately, less than half of new donors return to provide a second donation and fewer than 8% become committed donors. As a result, the nation's blood supply is highly reliant on first-time donors who must constantly be replaced because they typically fail to return. In addition to enormous ongoing recruitment costs, failure to retain first-time donors has important health implications, as repeat blood donors are less likely to be deferred for poor health and to transmit infections such as HIV, hepatitis B, and hepatitis C. Accordingly, the current proposal develops a promising new approach to donor retention, and specifically tests its efficacy among first-time, Group O, Rh negative (O-) donors whose red blood cells are in great demand for transfusion but are often in short supply. The current study examines the ability of a post-donation motivational interview and implementation intention intervention to enhance retention of O- donors. We have developed and pilot-tested a motivational interview (MI) designed to flexibly address individual barriers and deterrents to donor retention. We will explore the mechanisms of action of MI using key predictors of donation behavior as described by the Theory of Planned Behavior (attitude, subjective norm, perceived behavioral control, and intention). We will also examine the effect of MI with and without the addition of an implementation intention (II) intervention, a form of action planning that has been shown to enhance behavioral follow-through among those who express an intention to engage in a wide variety of health-promoting behaviors, including blood donation. Our primary outcome measure will be donation attempts in the one-year follow-up period. Additional outcome measures will include donation attitude, perceived behavioral control, and donation intention. Our primary hypothesis is that first-time O- donors who receive MI or II will have more donation attempts than control donors in the next year, and that donors who receive MI+II will have the highest retention rate. Donors who receive MI or MI+II will also demonstrate larger increases in donation attitude and perceived behavioral control compared to II and control donors, which will contribute to enhanced donation intentions and attempts. Finally, compared to controls and MI alone, donors who receive II or MI+II will show a stronger correspondence between their intention to donate again and their behavior. This project is significant, innovative, and timely because it (a) further develops a novel approach to donor retention that directly addresses individual donor barriers, (b) targets retention efforts to enhance the supply and improve the safety of much-needed O- blood, (c) examines specific, theory-driven mechanisms, and (d) incorporates action planning to bridge the gap between donation intention and behavior. This study will have an important public health impact by developing an intervention that can flexibly target donor retention efforts to encourage collection of specific blood products based on local, regional, and national patient needs.